Karyotype Variability in the Genus Radacridium (Orthoptera, Romaleidae, Romaleinae)

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The genus Radacridium (Romaleidae) is endemic in the Northeast region of Brazil and is chromosomally described here using specimens collected in the Agreste (R. mariajoseae) and in the Caatinga (R. nordestinum), State of Pernambuco. Both species presented 2n = 23, XO in males and acrocentric chromosomes. The two species can be distinguished on the basis of C-banding patterns and location of the nucleolar organizer regions (NORs). R. mariajoseae showed C-bands only in the pericentromeric regions of autosomes L1, M9, S10 and S11 and in the proximal regions of L₂. Chromsome X presented proximal and distal pericentromeric bands. R. nordestinum, in turn, has pericentromeric bands in all chromosomes and interstitial bands in pairs L₂ and M₅. The bivalent M9 corresponds to the megameric chromosome for the two species. Furthermore, R. nordestinum presented four chromosome pairs (L₃, M₄, M₆, M₇) bearing supernumerary heterochromatin segments that were absent in R. mariajoseae. In R. nordestinum a comparative analysis of standard karyotypes and karyotypes with an interstitial supernumerary segment in pair 4 revealed chiasma redistribution in all chromosome groups, with no change in mean chiasma frequency per cell. The nucleolar organizer chromosome was the X in R. mariajoseae and the L₂ pair in R. nordestinum. Cores and kinetochores stained identically in the two species. Taken together, the chromosome data show that these species are cytogenetically well distinct.